The present invention, in some embodiments thereof, relates to cardiovascular medical applications and, more particularly, but not exclusively, to a method, apparatus and system for predicting electro-mechanical dissociation or pulseless electrical activity.
Sudden cardiac arrest is a life-threatening condition. It is recognized that the percentage of individuals who are successfully resuscitated with intact neurological function following a sudden cardiac arrest is less than 10%.
A cardiac arrest is the cessation of normal circulation of the blood due to failure of the ventricles of the heart to contract effectively resulting in the cessation of blood delivery to the whole body. As a consequence cells of the whole body suffer injury resulting from hypoxia (oxygen starvation). Lack of oxygen supply to the brain causes victims to immediately lose consciousness and shortly thereafter stop breathing. Cardiac arrest is different from a heart attack (myocardial infarction). In a cardiac arrest the heart suddenly stops beating. In a heart attack, blood flow to a region of the heart muscle is disrupted. That region of the heart muscle deprived of blood flow suffers injury which might lead to cell death if blood flow is not restored promptly. During a heart attack, only part of the heart ceases to work properly, thereby compromising cardiac function, but not completely; the rest of the heart muscle continues to work promoting blood flow albeit the total work produced by the heart may be sometimes significantly diminished. However, heart attacks can sometimes lead to cardiac arrest in which the heart as a whole stops beating and ceases to promote blood flow into the systemic circulation.
In apparently healthy adults, cardiac arrest is often precipitated by ventricular fibrillation, which is most often associated with underlying coronary artery disease, but may also be associated with electrical abnormalities of the heart muscle originating in a region of the heart in which there is reduction of blood flow or disproportionate increase in oxygen demands in such region.
Cardiac arrest can also occur without ventricular fibrillation. The heart can stop beating because of asystole in which there are no electrical impulses originating from the heart, or because of Electromechanical Dissociation (EMD) which is a clinical condition with no palpable pulse or blood flow although coordinated ventricular electrical activity exists. During EMD, there is an adequate cardiac electrical rhythm but no effective cardiac pump action by the heart, so that no significant arterial pressure is generated spontaneously. Recently, the term Pulseless Electrical Activity (PEA) has been used for this condition.
There are numerous reasons leading up to EMD. Oftentimes the reason relates to a severe systemic condition which affects the heart as a component of multi organ failure. For example, EMD may occur in patients with severe septic syndrome, severe hemodynamic instability such as hypovolemic shock, severe metabolic acidosis, severe hypoglycemia, disseminated cancer and so on. In those cases, despite an electrical trigger to contract that heart's muscle cells (e.g., myocardium) fail to contract. For example, in severe acidosis the pH environment disrupts the normal contraction of myocardial cells; while in severe shock myocardial cells suffer form poor perfusion and hypoxia. In some cases, EMD occurs following treatment with a defibrillator, where a patient may exhibit an electrical pulse but not a physical pulse. It has been reported that less than 10% of individuals with post-shock EMD survive.
Cardiac arrest caused by asystole or pulseless electrical activity can also occur associated with existing cardiac disease, especially when severe heart failure has developed.
U.S. Pat. No. 6,440,082 to Joo et al., discloses a technique in which phonocardiogram (PCG) data electrocardiogram (ECG) data are analyzed for determining the presence of a pulse in the patient and determining whether the patient is in a state of PEA. The PCG data are evaluated to indicate the presence of a heart sound, and the ECG data are evaluated to indicate the presence of a QRS complex. If the time at which the QRS complex occurs is within an expected time of when the heart sound appeared to occur, a cardiac pulse is determined to be present in the patient. Joo et al. also disclose a technique in which the ECG data are evaluated to gate the heart sound detection process. Specifically, Joo et al. teach that if a heart sound is not detected following an R-wave, the patient may be in a state of PEA.
U.S. Published Application No. 20030109790 to Stickney et al. discloses a technique in which PEA is detected when a patient is determined pulseless and the patient is not experiencing ventricular defibrillation, ventricular tachycardia or asystole. According to Stickney et al., the presence or absence of a cardiac pulse is determined by evaluating fluctuations in an electrical signal that represents a measurement of the patient's transthoracic impedance; the presence or absence of ventricular defibrillation or tachycardia is determined by differentiating shockable from non-shockable cardiac rhythms according to the teachings of U.S. Pat. No. 4,610,254; and the presence or absence of is determined according to the teachings of U.S. Pat. No. 6,304,773. Stickney et al. also teach detection of PEA using ECG data wherein a state of PEA is detected when QRS complexes are repeatedly observed without detection of a cardiac pulse associated therewith.